Willis Tower is a skyscraper located in Chicago, Illinois.
It once held the distinction of being the tallest building in the world and is today among the top 20 tallest buildings around the globe.
The building is known for its bronze-tinted and black aluminum glass exterior.
Planning for the Willis Tower began as early as 1969. The tower was originally named the Sears Tower, after the retailer of the same name. At the name, Sears had a large number of employees in the Chicago area. In order to consolidate them in one place, the Sears Tower was conceived.
Skidmore, Owings & Merill were selected as the architects for the building. One of the key figures involved in the planning and construction of the Willis Tower was Fazlur Rahman Khan. Khan was the main structural engineer involved in the project. And he was instrumental in crafting a unique and defining outlook for the building.
The Willis Tower is among the first buildings to make use of ‘tubes’. It essentially comprises of 9 tubes, designed in a 3 x 3 matrix. The nine tubes rise concurrently up all the way to the 50th floor. The tube-like structures enabled Khan and SOM architects to ensure structural integrity of a building of exceptional height.
As the building rises up, the external tubes terminate and only the core tubes continue. From 90th to 180th floors, two tubes remain. This structure gives Willis Tower its iconic ascending shape.
The building has a total of 110 floors with 3 basement floors. It stands 442 meters of around 1450 feet tall. Together with the antennas installed at the top, the building’s height is 1729 feet. The building houses around 104 elevators.
One of the notable features of the Willis Tower is its observation deck, known as the Sky-deck. The deck is located on the 103rd floor. At a height of 1353 feet, it offers a stunning and sweeping view of the city. The structural design of the building allows it to sway in high wind conditions – and visitors can experience this extraordinary phenomenon at the observation deck.
More than 1.5 million people visit the Sky-deck every year. A stunning feature of the Sky-deck is the glass balcony. This all-glass structure allows visitors to stand on top of transparent glass and look down, getting a feeling of being in the air.
The Sears Tower: The History of Chicago’s Most Iconic Landmark Paperback – March 1, 2015
Sears Tower: A Building Book from the Chicago Architecture Foundation Hardcover – July 1, 2002